1. Field of the Invention
The present invention pertains to data storage devices where data is stored in a material that is reversibly convertible between detectable states in response to the input of energy. More particularly, the present invention pertains to a method for initializing a data storage device having a phase change data storage medium that is convertible between detectable states.
2. Description of the Background Art
Writable data storage or memory devices have been fundamental in furthering the technology driven information age. Included in writable data storage devices are the now highly commercialized and widely distributed phase change data storage medium.
An enormous consumer demand for writable and rewritable memory storage devices presently exists. Mass production of writable and rewritable memory storage devices in the form of phase change information data storage devices is currently underway to meet this consumer demand. For example, one well-known data storage device is the phase change optical memory disk. The typical optical memory disk may have a variety of layers to effect data storage, including a protective layer, a reflective layer, an upper dielectric layer, a phase change medium, a lower dielectric layer, and a disk substrate. The layers of the optical memory disk may also be formed in other configurations as well.
The phase change optical disk is a device with multiple detectable states that allow for the storage of data. For example, a phase change optical data storage device may have a chalcogenide memory material used as the active memory layer. The chalcogenide memory material may have an amorphous state, a crystalline state and varying intermediate states. When the phase change material is deposited on a disk, the material is formed in an essentially amorphous state. The crystallization characteristics of the material are different in first crystallization from all subsequent crystallizations. Therefore, the disk must be crystallized once before the disk is ready for use. This first crystallization is referred to as initialization. Thus, preparation of a newly manufactured phase change data storage device requires that the device be initialized into a crystalline state so that data can be reliably written and erased.
Present day disk initialization is typically carried out by directing a continuous laser beam along a track of an optical disk as the disk rotates. The laser energy is utilized to change the recording medium from an amorphous state to a crystalline state. An example of this process has been described in U.S. Pat. No. 5,768,221 which issued to Kasami et al. Therein is disclosed a method for initializing an optical recording medium by rotating a disk at a speed of 1000 rpm and directing a laser beam upon a small portion of the recording medium. The laser beam then moves from the inner most to the outermost circumference sections of the disk. Therefore, as the method serially initializes the disk, the method is relatively slow and does not lend itself to efficient mass production.
One attempt made at initializing the entire optical disk with a single energy exposure has been described in U.S. Pat. No. 5,684,778, which issued to Yamada et al. on Nov. 4, 1997. The Yamada patent discloses a process for initializing a phase change recording medium using flash light emission which drops the emission strength instantly to a zero level immediately after crystallization . The method teaches the necessity of exposing the disk to a single flash or single discharge of high intensity light for 0.1 to 10 msec with no residual exposure. The waveform described in the Yamada patent claims to fully and completely crystallize the phase change recording medium with the single energy exposure. Yet, as the patent admits, problems invariably arise in alleviating internal stresses and the tendency to cause warp and distortion in the disk, which problems the patent does not solve. Warp and distortion in the recording medium may provide a major cause of malfunction in disks and are therefore undesirable. To compensate for the warp created by the initialization method disclosed in the Yamada patent, said method requires a further step of unwarping or straightening an otherwise unusable disk. Additionally, internal stress can cause cracking and/or delamination of various layers within the optical disk. As such, methods of flash initialization, as presently known, are not desirable for large-scale commercial purposes.
Thus, present day methods for initializing phase change memory devices result in a reduction of production cycle time and increased manufacturing costs.
To address the above mentioned problems and others, the present invention provides a method for initializing a phase change information storage device including the steps of: providing a data storage device having a phase change data storage medium; exposing substantially all the phase change data storage medium with a first, energy exposure for about 1 xcexcsec or less. The first exposure is then followed by at least one additional energy exposure to complete initialization in a short period of time with reduced device damage and warp.
The initialization process may be accomplished by variations upon the present method, as will become evident from the ensuing disclosure, all of which are desired to be protected by the claimed invention, but in any event will require exposing the data storage medium to a first or pre-initialization energy. The pre-initialization energy is preferably delivered to the data storage medium as a predetermined waveform over a predetermined time with a power and spectral content suitable for initializing a memory device with reduced damage. Such a waveform preferably includes an initial pulse or burst of energy having a rise in intensity, a maximum intensity, and a decline in intensity over a period or duration of 1 xcexcsec or less. The waveform, energy level and spectral content act to pre-initialize the data storage medium. The initial pulse of energy is then followed by one or more additional exposures of energy, which complete the initialization process with reduced warp and device damage.
The method for initializing a memory device in accordance herewith is especially useful for initializing phase change optical disks, such as CDxe2x88x92RW, PD, DVDxe2x88x92RAM, DVDxe2x88x92RW, DVD+RW, multi-level optical disks, multi-layer optical disks, as well as others.
For a more complete understanding of the present invention, reference is made to the following detailed description and accompanying drawings.